Method of molding plastic material



Dec. 5, 1939. H. R. HUSTED METHOD OF MOLDING PLASTIC MATER IAL Filed Feb. 26, 1937 '2 Sheets-Sheet INVENTOR HARE Y A. Hus 7-50 ATTORNEY.

Dec. 5, 1939. H. R. HUSTED METHOD OF MOLDING PLASTIC MATERIAL Filed Feb.- 26, 1937 2 Sheets-Sheet 2 INVENTOR. HARRY R. Hu67f0 ATTORNEY.

Patented Dec. 5, 1939 UNITED STATES PATENT oi=FicE METHOD OF MOLDING PLASTIC MATERIAL new a Busted, St. Clair, Mich, assignor, by mesne assignments, to 'Ehe Standard Products gompany, Port Clinton, Ohio, a corporation of bio Application February 26, 1937, Serial No. 127,970

6 Claims. (Cl. 18-55) izing these weld lines never occurred in the same ri in rt 5, which in the present instance is go location twice. As a result, many articles, if not h w in r s ti n,

rejected, required a subsequent finishing or touch- Leading t t cavity 5 is a gate a which ing Operation 810118 these d lines in Order to ducts the material under pressure from an inproduce the desired appea a on the Surface jecting source through a suitable sprue ll.

Su h su u t fin shi p ra o s add greatly The material upon entering the cavity 5 nec g5 to the cost of the ar clesessarily divides into two oppositely flowing The principal Object the present inventien, streams F and 8 around the cross section of the t r f r lies in th provision of a m ld hav n insert 6 and concurrently tends to now length- 85 plurality 0? zones in Which e temperature wise of the insert, oittimes before completely enso aybe controlled independently o at the ow veloping the cross section or the insert. The so a p s y 0f the thermoplastic Coating can relative velocity of flow of these streams depends be controlled W h reasonable and Practical upon the relative resistance offered by the cavity its while in the mold. walls 3 and 4 and also the resistance ofiered by A correlative object is to provide a mold of this Y th surface of th insert a,

as character in which the temperaturesof the sepa- Such resistance to flow can be governed by the table Sect ons a e Co t ed independently of temperature of the material and of the cavity each other in a manner such that the weld line walls 3 and '3, Since the viscosity of the plastic will occur at the least conspicuous zone on the material varies inversely with the temperature or surface of the molded article. the material, it follows that a relatively low tem- I m Another object is to provide a mold capable perature causes the material to become more vis- 40 0! Consistently Producing a uniform high quality cous or more resistant to flow. Like all other or articles. flowing substances, it follows the path of least O e objects wi come appar nt fr m the resistance. Thus, if the temperature in certain follewing pecification in conjunc ion W the zones oi the mold cavity is lower than in other 4% accompanying drawings, in which: zones, the rate of flow in these zones of low tem- 1 is a p an v ew 0! a o d: perature is less than that in the higher tempera,- "Fis- 2 is e Vertifiel Sectional w taken S ture zones; Consequently, the portion of the stantisl y a o e a pl e i di ated by t e line mold cavity which is the hottest will be the first of Find; to become filled with material, and upon conso F s. 3 and 4 a e r d trasme tary c os tinued injection pressure on the material, the so sectional views through a mold showing the i relatively cooler portion of the cavity will be the Jected material in difierentstages of its travel; last to be filled. As a result, this relatively cooler Fig. 5 is a fragmentary sectionalview through portion of the mold cavity will inherently conamold showing an article of hardware positioned tain the meeting line of the difierent streams of therein;

This invention relates to an improvement in injection type molds and is more specifically directed to a method and means for controlling the fiow and meeting oi two approaching streams of thermoplastic material in a mold cavity, whereby the zone of the inherent weld line is controlled.

The preferred embodiment of the invention comprises a mold having separable mold sections, each of which is maintained at adifierent temperature for the purpose of effecting a control of the plasticity and flow oi the material whereby the welding line of the approaching streams of material is located in predetermined desired locations.

In prior injection type molds of this general character, no attempt has been made to control the location oi-the weld line in any manner. Consequently, the minute apparent scratches or cracks appearing on the surface and character- Fig. 6 is a bottom plan view of the article of hardware in Fig. 5, showing the position of the weld line at the underside of the piece; and

Fig. '7 is a fragmentary vertical sectional view through the mold and insert taken along a plane indicated by the line 'l? of Fig. 5.

For'purposes of illustration, one embodiment of the invention will be described in connection with the coating of asteering wheel rim, its application to other articles being readily apparent therefrom. n

Referring to Figs. 3 and 4, the mold is show comprising an upper mold section 6 and a lower mold section 2, the sections having cooperating recesses 3 and 4, respectively, which define a cavity 5 when. the mold sections are closed.

Positioned within the cavity 5 and held in spaced relation from the walls thereof in any suitable manner, is an annular steering wheel material, and by controlling the temperatures at 1 different zones independently of each other, the meeting line can be controlled. These tempera tures are preferably within the customary limits 1 utilized in practice, the higher temperatures be- 1 ing somewhat lower than the melting point of the material and the lower temperatures being of such a degree as'to effect the desired, flowretarding results.

' In the covering of steering wheel inserts or spiderswith thermoplastic material, it is desir- 1 through the ducts for the purpose of heating one i able to cause this meeting line to occur in the F least conspicuous zone on the surface, that is, on

' the under side of the insert.

cavity wall 4, which forms the under side of 'the finished wheel, may be maintained at a lower temperature than the upper cavity wall 3.

Therefore, the lower 1 To effect and maintain this. lower portion of. i thecavity at a relatively low temperature, consired temperature is passed, are provided in the duits in, through which thermal fluid at the de- 1 mold section 3 and in close proximity with the cavity wall 4.

; The upper mold section I is likewise provided 1 with similar fluid conduits l2 closely adjacent the cavity wall 3 for conducting fluid at a different and; preferably higher temperature than that,

flowing'through the conduit Ill for maintaining the cavity wall 3 at a different or relatively higher temperature than the cavity wall 4. Consequently, the resistance to flow of material in l the upper half of the mold cavity is considerably 1 less than that in the lower half by reason of the diiIerence in temperature in the two halves.

In operation, the stream of material from the gate 9, upon being injected into the mold cavity, divides into the pair of oppositely fiowmg streams I and 8 around the insert, as shown'in Fig. 1, the

1 upper stream .1 flowing at a more rapid rate 1 than the lower stream 8 for the reasons stated 1 7 6 above. Since'the temperature of the cavity wall 5 I 1 A is lower than the temperature of the wall 3,

5 it follows that the streams of material I and 8 1 will meet each other in the coolest zone of the: 1 cavity to form a weld line Hi. This zone is coni trolled in the manner above described and in the 1 exemplary showing is located approximately at,

1 the lowermost .portion of the cavity wallfl which j is the least conspicuous area on the entire steering wheel surface. Consequently, when the wheel 1 view of the operator of the vehicle.

To further assure that the weld takes place in 3 is installed, the weld line is concealed from'the 1 the desired location, the insert 6 may be off-set 5 l with respect to the cavity so that the portion of the insert where the weld occurs is relatively:

1 close to the cavity walls. Thus the insert G'may be nearer the wall of the recess 4 than it is to 1 the recess 3. This restricted portion of the cav- I ity will offer greater resistance to flow of the material, and as a result, the material in the stream I will flow a greater distance around: the' top portion of the insert than the stream i'fiowing around the lower portion. Thus it will 1 be seen that contracted portions of the cavity can be employed to assist in controlling the location in which the streams of material willj meet, which is more fully described in an appli- I cation of Dwight M. Anderson, Serial-No. 132,849, 1

I filed March 24, 1937.

shown in Patent No. 2,043,584, issued portion of the cavity while cooling another portion, as desired.

The principle of controlling the location of the weld line is equally applicable to other articles, such as an automobile window operating handle. ll, shown in Fig. 3. In this particular article, it is desirable that the weld line l8 be positioned on the lower surface IQ of the handle so as to be on the side nearest, the door and in the least conspicuous zone when in installed position on an automobile door. Therefore, the lower mold section 2|! is provided with the passages 2| for conducting a cooling medium therethrough to maintain the temperature of this portion of the .cavity at a certain degree. The upper mold section 22 is likewise provided with conduits 23 for v conducting relatively warrn thermal fluid therethrough to maintain the upper section of the mold cavity at a higher temperature than the mold section 20.

Thus it will be seen from the above da'cription that a novel, effective and inexpensive method and means for controlling the position of the weld line on the surface of the finished article has been provided. By the use of this invention, it is possible to maintain a uniform quality'of articlesand greatly reduce the quantity of articles heretofore scrapped by reason of the objectionable weld line occurring at a conspic uous zone on the surface of thearticles. The

temperatures of the mold sections may be controlled and maintained automatically or manually, as desired.

Although a limited application of the invention has been shown and described for purposes of illustration only, it will be apparent to those Having thus described my invention, whatv I' claim is:

1. In the injection molding of articles of thermoplastic material wherein material injected into the mold is caused-to flow in different directions and subsequently to approach and unite,

the method of controlling the location of the weld produced between the relatively approachin; portions of the material, which comprises maintaining said relatively approaching portions atdiflerent temperatures within the mold cavity to provide different rates of flow thereof and controlling said temperatures for controlling the meeting location 'of the portions whereby the approximate location of the weld is predetermined.

2. The method of controlling the location of weld in the injection molding of thermoplastic material wherein a stream of the material in- I jected into the mold is divided and portions thereof caused to flow in difierent directions and subsequently to approach each other and reunite at a hlg'her'temperature than other portions for 75 controlling the distance of travel of said portions respectively, whereby the zone of meeting of said difierent portions within the mold cavity and the resultant weld line is approximately predetermined.

3. The method of controlling the location of the weld in the injection molding of material the plasticity of which depends upon the degree of heat applied thereto, and wherein material injected into the mold is caused to flow in different directions and subsequently to approach and unite, which method comprises injecting the material in plastic condition into a mold cavity and concurrently maintaining predetermined portions of the walls of the mold cavity at different temperatures from other portions whereby the rate of flow of the material past said predetermined portions and said other portions is different.

4. The method of controlling the location of the zone of confluence of a plurality of streams of thermoplastic material during the injection mold coating of an insert which consists of supporting the insert in the mold cavity in spaced relation from the walls thereof, injecting material in the plastic state through an entrance into the space between the insertand the cavity walls, causing the material to divide adjacent said entrance into streams which flow in difierent directions within said space and around the insert and then to converge and meet in another portion of said space remote from the entrance, controlling the location of said meeting of the streams of material and resultant weld by maintaining the material of the stream of material flowing in one direction from the point of injection at a different temperature from that of the stream of material flowing in a diflerent direction from the point of injection.

5. The method of controlling the location of the zone of confluence of a number ofstreams of thermoplastic material flowing in a mold cavity during the injection mold coating of an insert which consists of supporting the insert in the mold cavity in spaced relation from the walls thereof, injecting material in the plastic state through an entrance into the space between the insert and the cavity walls, causing the material to divide adjacent said entrance into streams which flow in different directions around the insert subsequently causing convergence and meeting of the streams to form a weld remote from said entrance, and controlling the location of said meeting of the streams of material and the resultant weld by maintaining different portions of the cavity walls at diflerent temperatures'.

6. The method of controlling the location of the zone of confluence of a plurality of streams of thermoplastic material during injection molding of the material in a manner tending to cause such confluence of separate streams within the mold cavity, comprising injecting the material in plastic, condition into a mold cavity, maintaining portions of the mold cavity walls at a certain temperature and other portions of the mold cavity walls at a lower temperature while the material is flowing within the cavity under pressure and maintaining the material under pressure in the cavity for a predetermined interval after the cavity is filled.

HARRY R. HUSTED. 

